Pressure Pain Threshold Evaluation of the Effect of Spinal Manipulation in the Treatment of Chronic Neck Pain

Authors Abstract

Nine subjects with chronic mechanical neck pain syndromes were evaluated for pressure pain
threshold (PPT) over standardized tender points in the paraspinal area surrounding a manipulable spinal lesion. The subjects were then allocated randomly to an intervention consisting of either an
oscillatory mobilization of the cervical spine (n=4), which was designated as the control procedure, or a rotational manipulation of the cervical spine (n=5). An assessor-blinded re-evaluation of
the pressure pain threshold levels was conducted after 5 minutes. In the group receiving a manipulation the mean increases in pressure pain threshold ranged from 40-56% with an average of 45%. In
the control group no change in any of the pressure pain thresholds was found. These results were analyzed using ANOVA and were found to be statistically significant (p < 0.0001). This study
confirms that manipulation can increase local paraspinal pain threshold levels. The use of the pressure pain threshold meter allows for the determination of such a beneficial effect in the deeper
tissues.

Editors Summary

Very few clinical trials have been produced to provide evidence that manipulative treatment
by chiropractors is beneficial to patients with neck pain. The senior author of this study, Howard T. Vernon, conducted clinical analog studies in which the results of a single manipulation were
compared to control procedures. In the first study, a single thoracic manipulation produced a significantly higher rise in cutaneous pain tolerance levels than the
shashared/stockpages/cp/conditions/neckpain/m/manipulation group. In the second study, a single manipulation of the cervical spine produced a modest increase in plasma beta-endorphin levels while
control and sham procedures dropped. These studies support the idea that pain relief occurs subsequent to manipulation, and to the theory that this pain relief is a result of reflex mechanisms
activated by the thrust. The reflex mechanisms can be described as afferent bombardment from the articular and myofascial receptors which produces pre synaptic inhibition of segmental pain pathways
and possibly activation of the endogenous opiate system. The purpose of this study is to extend this earlier work to prove that a single manipulation would produce a significantly higher rise in
pressure pain threshold levels in the paraspinal area surrounding a spinal fixation as compared to a control procedure. In this study, a more accurate device is used, the pressure threshold meter.
The advantages are that this device can objectively measure pressure pain threshold over tender points in muscles as well as measure functional changes in the deeper tissues around a joint.
Subjects were chiropractic patients diagnosed with chronic mechanical neck pain for an average duration of less than 3 months. The research treating physician assessed for joint dysfunction of the
cervical spine, and marked the "fixated" or hypo mobile segment. The treater left the room and the assessor entered to conduct a PPT assessment of four tender points above and below, and on each
side of the fixated level. The points were consistently measured as:

ipsilateral to the clinically painful side, slightly below the fixation;

ipsilateral, above;

contra lateral, above;

contra lateral, below.

Two measurements were taken at each point and the assessor left the room. The treater entered and applied the appropriate treatment of either a rotational mobilization with gentle oscillations into
the elastic barrier, or a rotational manipulation (high velocity, low amplitude thrust). All subjects were asked if they felt pain and if they believed that they had received a "real" treatment.
Finally, the blinded assessor re measured the tender points twice after 5 minutes.

Results revealed a statistically significant rise in pressure pain threshold ranging from 40-55% in all four points around the fixation level in the manipulation group compared to virtually no
change in the mobilization group. All subjects that were manipulated reported no pain and regarded the manipulation as a "real" treatment. Of the four mobilized subjects, three reported no pain and
none regarded the mobilization as "real". These findings are behavioral as related to the subjects perception of pain, but the underlying mechanism of spinal reflexes causing pain threshold changes
is still supported especially since no subject felt pain from the manipulation.

In conclusion, the pressure pain threshold meter has proven to be useful in objectifying the effect of manipulation versus mobilization in the cervical spine of subjects suffering from chronic
mechanical neck pain, and these findings support the theoretical mechanisms proposed to explain the effects of spinal manipulation on spinal pain.